Composition of matter for molds



Patented Mar. 10, 1925.

UNITED STATES PATENT orrlca.

WILLIAM D. MOORE, OF BIRMINGHAM, ALABAMA, ASSIGNOR TO AMERICAN CAST IRON PIPE COMPANY, OF BIRMINGHAM, ALABAMA, A CORPORATION OF GEORGIA.

COMPOSITION OF MATTER FOR MOLDS.

No Drawing. Original application filed March 1, 1923, Serial Rim 622,082. Divided and this application filed March 8, 1923. Serial No. 623,650.

To all whom it may concern:

Be it known that I, WILLIAM D. Moons, a citizen of the United States, and resident of Birmingham, in the county of Jefferson and State of Alabama, have invented certain new and useful Improvements in Composition of Matter for Molds, of whlch the following is a specification.

This invention relates to the art of centrifugally casting hollow metal bodies and more particularly to the making of s -h bodies on a refractory material such as sand molds; and has special reference to the pro vision of a new composition of matter employed for the sand lining of the mold and to the resulting refractory mold, this application being a division of my application Serial No. 622,082, filed March 1, 1923.

In the centrifugal casting of metal tubes with the use of refractory such as sand molds, the molten metal is discharged into a flask lined with a refractory material usually provided with a facing on the inner surface thereof, one well-known process comprehending the utilizat on of a green, moist or unbaked sand lining. Castings obtained from the centrifugally operate green sand molds combine the desirable properties of ordinary sand cast metal, such as the superior resistance to corrosion an other actions which tend to disintegrate the metal and shorten the life 0f the p1pe, w th the high qualities of centrlfuga-lly cast p1pe or tubes such as the greater denslty and solidity and consequent greater strength and modulus of elasticity. Although the green sand centrifugal mold process is capable of yielding a superior 1ron product, the processes heretofore proposed have not met with commercial adoption, due to the conditions that have been encountered 1n centrifugally casting on these sand molds, which conditions have heretofore been regarded as unavoidable and have not been successfully solved.

Among the more prominent problems resented in this art of centrifugally castmg on refractory molds were for example the diiiioulty of preventmg the cutting and washing of the sand by the action of the molten metal discharging into and flowing through the mold; the further difiiculty of producing a clean casting without pocketed or honeycomb defects; the further troubles accompanying the use of sand mixtures with wh1ch .the facings used were not properly united or associated and which facings were picked up by and washed and carried along with the flowing metal, resulting not only in the leaving of blemishes on the surface of the casting, but in the production'of a prohibitive amount of scruff; and such further mechanical objections as the instability of the sand lining when the mold is subjected to rotation at high speeds. To obvlate these and other difficulties and drawbacks and to successfully produce economically that casting product obtainable in a centrifugally operated sand mold is a prime desideratum of my present invention.

Among the principal objects of my present invention are more specifically the provislon of a composition of matter or a sand mixture for the refractory lining of the mold, and the provision of a mold embodyng such a lining which permits of obtainmg clean non-defective castings, which is not subject to the liability of being cut and wasned by the molten metal introduced into (1 the mold, which composition or mixture is furthermore of a nature such as will obviate mechanical drawbacks found in prior d practices and with which certain facing materials may be properly united to provlde a hardened mold wall capable of rendering efficient service in a casting operation.

As the result of extended experimentation on the characteristics and behaviour of green or moist sand linings in centrifugally operated molds, I have found that the moisture content of the sand mixtures plays a highly important role in the production of a meritorious casting, the sand if in too dry a state having the objection of not possessing bonding power suflicient to support itself to withstand the cutting and washing action of the molten iron and the centrifugal action of the mold, and if in too moist a state giving rise to too copious a generation of steam and gas, more than the sand is capable of taking care of, with the result that the steam is blown into the metal instead of out through the mold, making a honeycomb or pocketed casting. I have discovered that with a certain moisture content in the sand mixture,-

and further with certain constitutents thereof the fluid metal, and to obviate on the other hand the objectionable degree of steam generation. To withstand any tendency to destruction by the hot flowing metal in the mold, the sand mixture employed for the mold linin should also have certain constituents w ich combine to provide sufficient cohesive power to preserve the integrlty of the mold, to be of a sufficiently refractory nature to withstand the heat of the molten metal, and to have sufficient porosity to permit the easy escape of the gases and steam during a casting operation.

To produce a sand mold having these characteristics, I employ a sand mixture havin the composition presently to be describe this sand mixture possessing a moisture content preferably of from 7% to 11% calculated on the weight of the dry sand, the centrifugally operated mold or flask being lined with this sand mixture. I have found the following mixture to give very desirable results:

Percent. Silica sand 50 Sharp sand 35 Molding sand 15 The silica sand employed is an even grain sand consisting) of quartz in rather rounded grains caused y the attrition of the grains in the process of formation of the deposit, it having been formed by long-continued rolling and washing of the quartz by the waves. This silica sand should contain at least 95% of silicon dioxide. The sharp sand employed is high in silica but is not subjected to so much rolling as silica sand.

e grains are angular, having sharp corners and ends, and the sand usually contains from about 10% to 20% of feldspar and from 4% to 10% of clay. The molding sand used is high in clay and usually ferruginous and may contain 30% to 50% of clay and 10% to 20% of feldspar.

The rational analysis of this sand is substantially as follows:

Per cent. Quartz to Glay 5 to 10 Feldspar 5 to 10 .Uncombined water 7 to 11 the water being calculated on the weight of the porosity of the mold, this being of prime importance in allowing the escape of the gases through the mol The clay substance acts as a binder holding the grains of uartz together, and functions to preserve t e integrity of the moldv surface. If used to excess, however, it tends .to decrease the porosity by closing u the inter-c stalline pores of the sand, and hence should e kept as low as possible and still hold the grains of quartz together. The proportion of clay in my mixture has been found to yield very satisfactory results.

The feldspar composes the alkali-bearing minerals of the sand, has a low melting point, and tends to fuse or burn to the iron. It is altogether undesirable, but is contained in all commercial sands and clays and is reduced to a minimum in the mixture of my invention.

The water or moisture used in the mixture is the free or uncombined water determined by drying at 110 0., and does not refer to the Water of combination substances. This in redient is necessary to obtain the proper dlstribution of the clay, giving it t e necessary mobility and adhesiveness and enabling it to coat each individual grain of sand sothat it adheres to the others. This water or moisture performs the further function of giving a slight chill to the outer layer of iron and thus assisting in preserving the mold from the action of the hot iron. Too much moisture such as a quantity over 11% will generate more steam than can escape through the body of the mold or sand, and will cause defective castings; while not enough moisture, as for exam Is a moisture content under 7%, will not istribute the clay sufliciently and thus will allow the sand to wash or be torn out of the mold by the impinging stream of molten iron. A further important function of the moisture content of the sand is to furnish the required moisture for the facing material I prefer to employ for the mold, as will be described presently, so as to cause the material to set properly to form a membraneous or shell-like facing for the mold.

As heretofore noted, it is highl desirable to provide the sand lining of sue a nature or composition as to properly combine or be united to the facing WhlCh I use for coating the surface of the sand lining, in order to prevent the facing from being icked up and washed by the flowing meta, and in order further to provide a mold wall which is hard and dense and resists the cutting action of the iron. I have found that the sand mixture or composition of my invention may be used with great advantage in association with a facingl results. In t 0 preferred practice of my invention I employ a owdered substance and preferably powdered natural cement, this bepresent in all clay material for producing these ing a pulverized product resulting from the calcination of an argillaceous limestone at a temperature only sufficient to drive off the carbon dioxide. This powdered cement is applied to the surface of the sand lining in the flask, and immediately the application is made the powdered cement begins to absorb moisture from the moist sand linin and chemically react to quickly take an initial set, producing instead of a soft powdered facing a rather tough membraneous or shelllike facing which has a high resistance to the cuttingaction of the iron and intimately unites with the surface grains of the sand lining, and forming therewith practically an integral structure, producing a comparatively dense and hard mold wall.

' While I have shown the preferred form of my invention, it will be obvious that many changes and modifications may be made therein without departing from the. spirit of the invention, defined in the follow: ing claims.

I claim:

1. A composition of matter for sand molds comprising a green sand mixture having 80% to 85% of quartz, to of clay, 5% to 10% of feldspar, and 7% to 11% of water.

2. A composition of matter for sand molds comprising a moist sand mixture composed of 50% silica sand, 35% sharp sand, and molding sand.

3. A composition of matter for sand molds comprisin a moist sand mixture composed of 50% silica sand, sharp sand, and 15% molding sand, the mixture having about 7% to 11% of uncombined water calculated on the weight of the dry sand.

4. A hollow sand mold for centrifugally casting hollow metal bodies provided with a sand lining com osed of a moist sand mixture having from%% to 11% of uncombined watgr calculated on the weight of the dry sau 5. A hollow sand mold for centrifugally casting hollow metal bodies provided with a sand lining composed of a sand mixture having from 80% to 85% of quartz, 5% to 10% of clay, 5% to 10% of feldspar, and 7% to 11% of water.

6. A sand mold for centrifugally casting hollow metal bodies provided with a sand lining composed of a green sand mixture having 50% silica. sand, 35% sharp sand, and 15% of molding sand.

7. A sand mold for centrifugally casting hollow metal bodies provided with a sand lining composed of a green sand mixture having 50% silica sand, 35% sharp sand, and 15% of molding sand, said mixture having about 7% to 11% of uncombined water calculated on the-weight of the dry sand.

Signed at New York city, in the county of New York and State of New York this 21st day of February, A. D. 1923.

WILLIAM D. MOORE. 

